You can use any Mod site that you can find.
I recommend to use NexusMods [www.nexusmods.com]

If you want to Install an Outfit Mod than it's pretty easy
Head to your South Park Install Directory
--> C:\Program Files (x86)\Steam\steamapps\common\South Park - The Stick of Truth

Then open the data folder

In the data folder create a new folder called "gui"

After that open the gui folder and move all files from your Outfit mod into the folder

And that is how to Install an Outfit Mod
Here a Screenshot how the Gandalf Outfit looks ingame

What with Other Mods is meant, is the Uncut Patch for the German version which can be found on Nexus Mods [www.nexusmods.com] as well.

Installing this Patch is even easier than the Outfit Mod, you just have to move the files that you downloaded into your game folder and thats it.

A Mod you should install is "Skip Opening Intros" with this mod you can instantly start the game without waiting the Intros for 10 Seconds when launching the game here is the Download[www.nexusmods.com]

I Hope this Guide helped you guys out!
If you have any Questions let me know